1. Field of the Invention
The present invention relates to a contents recorder/reproducer that can protect contents that are recorded and reproduced.
2. Description of the Related Art
Although a digitized audio-visual work called contents has conventionally been difficult to handle because of its large size, a recent advance in the high-density recording/reproduction technology makes contents distribution more popular.
One of the merits of digitization is that information is not degraded even if copied. On the other hand, an infringement of a reproduction right through illegal copies has become evident.
Contents encryption is efficient for preventing illegal copies.
For example, when recorded on a digital video disc (DVD), video information is encrypted to prevent it from being reproduced unless the information is decrypted using a predetermined procedure.
In this type of encryption, contents to be recorded are encrypted in advance using, for example, predetermined key information. In general, a sequence of synchronous blocks, each with a predetermined length, is formed on a recording medium such as a DVD and the encrypted contents are recorded in units of synchronous blocks. Each synchronous block has a block address that uniquely identifies the synchronous block. The block address is recorded in advance at the start of each synchronous block.
Contents are recorded on, or reproduced from, a recording medium, for example, by the micro-controller and the file system software that control the whole recorder/reproducer.
When contents are recorded, encrypted contents are divided into synchronous blocks and are sequentially recorded while searching the block management table on the recording medium for synchronous blocks into which contents may be written. A similar procedure is used to record key information, which is used to encrypt the contents, on the recording medium.
When contents are reproduced from a recording medium, the same key information as that used for encryption is used for decryption. To do so, the key information recorded in advance on the recording medium is read and the key information that was read is used to decrypt contents read from the synchronous blocks.
The encryption technology described above encrypts contents to be recorded on a recording medium and hides the key information and the encryption algorithm to prevent the contents, read from the recording medium, from being copied to another recording medium.
However, if the encryption algorithm is analyzed and the key information is read from the recording medium, the encryption technology described above cannot prevent the contents from being copied.
In addition, the contents such as those described above are large in size, meaning that there is a large amount of data encrypted with a single key from the viewpoint of encryption algorithm analysis. Therefore, it is required to make the analysis of the algorithm more difficult.
Another disadvantage in using a single key for encrypting the whole contents is that, once the encryption algorithm is known, the whole contents may be decrypted by the single key.